The present invention relates to a biomass gasification gas purification system, a biomass gasification gas purification method, a methanol production system, and a methanol production system method that can efficiently use biomass as a feedstock and can acquire a clean gas feedstock usable for fuels or for producing liquid fuels such as alcohol.
Generally, biomass refers to organisms (for example, agricultural products or by-products, wood, or plants) that can be used as an energy source or an industrial material, and is generated by an action of solar energy, air, water, soil, and the like. Therefore, biomass can be reproduced unlimitedly.
Use of the biomass enables production of a clean energy source such as gas and methanol for fuels. Furthermore, biomass as waste can be treated, which contributes also to environmental cleanup, and biomass to be newly produced can be grown by photosynthesis while fixing CO2. Because CO2 in the air does not increase, the use of biomass leads to suppression of CO2, and thus it is a favorable technique.
As biomass to be fed, it is preferable to feed produced or discarded biomass after being pulverized and dried. In the present invention, biomass refers to biological resources (for example, agricultural products or by-products, wood, or plants) that can be used as an energy source or an industrial material and, for example, plants such as sorghum, Napier grass, and Spirulina, and wood such as Japanese cedar, broad-leaved tree, and bark are used (Patent Literatures 1 and 2, and Non Patent Literature 1).
Meanwhile, gas produced by using the biomass as a feedstock contains fine particles, tar components, hydrogen sulfide, chlorine, and the like, and thus it is not suitable to use the gas as it is as gas for synthesizing a liquid fuel using a synthetic catalyst or an energy source for fuel cells. Accordingly, a method of removing minor components such as the fine particles, the tar components, the hydrogen sulfide, and the chlorine has been devised by using a separation device and a gas purification device. As a source gas for acquiring the liquid fuel and the energy source for fuel cells, for practical operation, the minor components need to be reduced to allowable content limits of tar, which is less than 1 mg/Nm3, and of sulfur content, which is less than 0.1 ppm. However, in the existing biomass gasification system, sufficient reduction of the minor components has not been realized yet.
Furthermore, the processing volume of the biomass gasification system is several hundred tons per day, which corresponds to a small-sized or medium-sized plant as compared to a typical gasification system using fossil fuels. In such a small-sized or medium-sized gasification system, it is preferable to include a simple and inexpensive gas purification line, which is an essential requirement in a so-called decentralized plant. Also in this regard, the existing biomass gasification system has not realized a simple and inexpensive gas purification line yet.
Conventionally, therefore, a biomass gasification system including a separation unit such as a cyclone that removes dust in produced gas gasified by a biomass gasification furnace, a cooler that cools dust-removed gas, and a gas purification device that purifies the cooled gas has been proposed (Patent Literature 3).
In the conventional gas purification device for biomass gasification gas, biomass is temporarily stored, and cooled produced gas having passed through the cooler is caused to pass through the gas purification device, where tar components contained in the cooled produced gas are adsorbed. Tar-adsorbed biomass from which the tar has been adsorbed is carried to a biomass feed unit by a carrier unit as purified gas.
There is another proposal of a fixed-bed removal device to which a remover layer for removing tar components is fixed (Patent Literature 4).